1. Field of the Invention
This invention relates to a ballpoint pen tip, manufacturing method therefor and ballpoint pen using it. More specifically, the present invention relates to a ballpoint pen tip rotatably holding a ball at the front end thereof by a plurality of inwardly projecting portions for a ball receiving seat which is formed by inwardly compressing and deforming the periphery of a neighborhood of the front end of a metallic pipe and a front end edge portion which is formed by inwardly compressing and deforming the front end of the pipe, a manufacturing method and a ballpoint pen using it.
2. Description of the Related Art
U.S. Pat. No. 4,457,644 discloses a conventional ballpoint pen tip rotatably holding a ball at the front end thereof by a plurality of inwardly projecting portions for a ball receiving seat which is formed by inwardly compressing and deforming the periphery of the neighborhood of the front end of a metallic pipe and a front end edge portion which is formed by inwardly compressing and deforming the front end of the pipe.
However, this conventional ballpoint pen tip does not take into account the thickness of the metallic pipe. Namely, the thickness of the pipe with respect to the ball size is set to be relatively thin so that the side of the metallic pipe can be easily compressed and deformed. Accordingly, a ball receiving seat does not have a sufficient strength due to the thinness of the inwardly projecting portion. During writing, since the ball receiving seat can not support the ball when a strong writing force is applied, it may be spread outwardly by the ball. Therefore, the ball bites at the ball receiving portion, thereby preventing its smooth rotation, and the ball gradually falls into the pipe, thereby losing a stable and smooth writing feeling. The smaller the ball size is, the more this phenomenon occurs.
Further, the top portion of the inwardly projecting portion of the conventional ballpoint pen tip has a relatively small radius of curvature. Accordingly, the surface of the top portion of the inwardly projecting portion is easily cracked by the compressing and deforming. Therefore, the cracking gives a user an unpleasant feeling with the ball rotation during writing.